1. Field of the Invention
The present invention relates to an imaging apparatus such as an electronic still camera including an imaging device for converting the light of a subject into electric signals.
2. Related Background Art
FIG. 1 is a sectional view showing one example of a conventional imaging apparatus which employs a CCD defined as a solid state image sensing device. FIG. 2 is a sectional view taken substantially along the arrowed line II--II of FIG. 1.
Referring to these Figures, the numeral 1 represents an image forming unit including a plurality of lenses. A quarter-wave plate 2 and a beam splitter 3 are disposed in rear of (right side in FIG. 1) of this image forming unit 1. This beam splitter 3 is fixedly bonded to the upper surface of a holding member 6 assuming a plane-parallel configuration. The holding member 6 is placed on a mounting surface 7b formed at the rear part (right side in FIG. 1) of a housing 7 and fixed with machine screws 8. Each machine screw 8 is inserted into a through-hole 7a penetrating the mounting surface 7b of the housing 7. The image forming unit 1 is fixed to the front part of the housing 7 by use of a machine screw 13.
Further, two CCDs 4, 5 are respectively provided upwardly and backwardly (right side in FIG. 1) of the beam splitter 3 through crystal filters 11, 12. The CCDs 4, 5 are, as known well, composed of a multiplicity of pixels arrayed one-dimensionally or two-dimensionally. These CCDs 4, 5 and crystal filters 11, 12 are fixed respectively to CCD holding members 9, 10 with machine screws 29. These CCD holding members 9, 10 (only the CCD holding member 9 is depicted) are attached to the housing 7 through height adjusting washers 15 as well as through machines screws 14.
Next, an imaging operation of the thus constructed imaging apparatus will be explained.
The quarter-wave plate 2 removes vertical and horizontal components of linearly polarized light, luminous fluxes of which have been condensed in the image forming unit 1. Subsequently, some of the luminous fluxes are reflected upwards by the beam splitter 3, penetrate the crystal filter 11 and are thereafter incident on the CCD 4. On the other hand, the luminous fluxes which have passed through the beam splitter 3 penetrate the crystal filter 12 and are incident on the CCD 5. Then, luminance information is read from the CCD 4 by means of an unillustrated electric circuit, while color information is read from the CCD 5. The information is also recorded in an unillustrated recording medium.
In the imaging apparatus described above, positional adjustments of the CCDs 4, 5 are important. As explained before, the luminance information is read from the CCD 4, while the color information is read from the CCD 5. Hence, if the positions of the CCDs 4, 5 deviate, it may happen that the luminance and colors of the different pixels correspond to each other when reproducing a color image on the basis of the luminance and color information. This may lead to a possibility that the image quality declines.
The positional adjustments of the CCDs 4, 5 require an adjusting allowance on the order of 1 mm at the maximum depending on variation caused when manufacturing the CCDs, 4, 5. Then, an accuracy of the positional adjustment is required to be less than or equal to a half of a dimension of a minor side of each of the pixels constituting the CCDs 4, 5 in terms of preventing the luminance and colors of different pixels from corresponding to each other. As one example, when a dimension of the minor side of the pixel is set to 4 .mu.m, the accuracy of the positional adjustment is required to be .+-.2 .mu.m or less. This is, it can be understood, a highly accurate positional adjustment.
The positional adjustments of the CCDs 4, 5 have hitherto involved the steps of determining the reference plane in the optical axis direction by use of a collimator (level vial) and properly selecting a thickness of the height adjusting washer 15; and, in the direction orthogonal to the optical axis, i.e., the direction along the light receiving surfaces of the CCDs 4, 5 the adjustments are made by effecting the positioning by use of a jig (illustration is omitted).
For the positional adjustments of the CCDs 4, 5 in the conventional imaging apparatus, however, it is required that the height adjusting washer 15 having an adequate thickness corresponding to each of the CCDs 4, 5 be properly selected every time the positional adjustment is performed. The workability of fabrication is not favorable, and it takes a long time for the work. Besides, there arises such a problem that a well-experienced operator is needed for selecting the washer 15. Further, when clamping the machine screw 14, the CCDs 4, 5 themselves are moved by this clamping force. This results in such a problem that the highly accurate positional adjustments are hard to perform.
Proposed as a means for obviating those problems was a technique of inserting a wedge member in a gap between the CCD and a spectral prism, positioning the CCDs by protruding or retracting this wedge member and thereafter fixing the CCDs with a bonding agent (Japanese Patent Laid-Open Application No. 2-140067). Alternatively, there was proposed a technique of connecting a solid state image sensing device directly to a prism by soldering (Japanese Patent Laid-Open Application No. 2-152376).
However, the technique of fixing the CCDs to the spectral prism with the bonding agent presents the following problems. Considering the adjusting allowances of the CCDs, it is necessary to secure the maximum bonding agent thickness on the order of 1 mm. When a thick bonding agent layer is provided as described above, and if the shrinkage factor concomitant with the hardening of the bonding agent is approximately 5%, there is a possibility in which the CCDs move as much as 50 .mu.m at the maximum. This causes a problem wherein a sufficient accuracy of the positional adjustment can not be secured. On the other hand, the technique of connecting the solid state image sensing device directly to the prism also has a similar problem because of the solder being shrunk with a cool-off of the solder.